The disclosure relates to a hydraulic control arrangement for a plurality of hydrostatic actuators or loads of a mobile working machine with neutral circulation.
With such control arrangements the different actuators are supplied by means of a respective valve arrangement from a common circulating line that connects a pump to a tank of the control arrangement. If no actuator requires pressure medium, a continuously circulating volumetric flow from the pump to the tank—the so-called neutral circulation—is possible with minimal energy consumption. Therefore the pump can be implemented as a constant pump that is simple from the equipment technology and control technology viewpoints.
With control arrangements with circulating lines, a first principle is known by which the volumetric flows of the different actuators that may be required are branched from the circulating line in parallel with each other. The publication “Hydraulics in Mobile Working Machines” of 27 Jan. 2014 of the applicant shows such a control arrangement in section 10.4.2. Its circulating line runs in a no circuit past the different valve arrangements by means of a (common) pressure compensator, which is opened in the event of non-operated actuators in order to thus enable the low-resistance neutral circulation.
According to a second principle, for neutral circulation the circulating line runs through the valve arrangements of the different actuators so that the valve arrangements are connected in series with each other.
The publication “Load-Sensing Control Block of Sandwich Plate Construction SB23-M” RD 66130 of the applicant of August 2013 shows said second principle with a constant pump and with only one actuator on page 3/24 on the left at the bottom. There by means of a directional control valve, in which the metering port for determining the speed of the actuator is integrated, the forwarding of the volumetric flow in neutral circulation is also enabled if the actuator is not to be supplied. By the continuous variability of the directional control valve, forwarding of some of the volumetric flow delivered by the constant pump that is not required by the actuator into the neutral circulation is possible if the actuator is to be moved slowly, for example.
In the documents U.S. Pat. No. 7,284,371 B2 and US 2011/0158830 A1, control arrangements for a plurality of actuators are shown that have neutral circulation that is passed through the valve arrangements of the different actuators. More precisely, the neutral circulation passes through respective directional control valves, whose valve pistons are in a central position (open center) in this case. Even if the neutral circulation of such control arrangements enables the use of a constant pump, variable pumps are provided with both of said documents.
Furthermore, it is known from the prior art to integrate an individual pressure compensator in each valve arrangement in the case of a control arrangement for a plurality of actuators of a mobile working machine having a variable pump. More precisely, an individual pressure compensator is associated with each metering port, so that a respective flow regulating valve is formed. This enables a volumetric flow to the respective actuator that depends on the opening cross-section of the metering port and that is independent of the load pressure of the respective actuator, whereby a high level of user friendliness results for the driver of the mobile working machine during the operation and control of the actuator.
In the publication “LUDV-Control Block of Sandwich Plate Construction” RD 64125 of the applicant of February 2011 on page 4/24 at the top, and in the already mentioned publication “Load-Sensing-Control Block of Sandwich Plate Construction SB23-M” RD 66130 on page 9/24 on the right, such a valve arrangement with an individual pressure compensator for supplying an associated actuator is shown in each case. Each valve arrangement including the individual pressure compensator is combined in a valve disc, a plurality of which are grouped in a control arrangement. In both documents a common pump line of the control arrangement runs through each valve disc, from which a respective channel branches to the valve arrangement of the respective valve disc.
It is a disadvantage of such control arrangements for a plurality of actuators that so-called load sensing lines are necessary, in which the pressure of the most highly loaded actuator is determined Depending on said pressure, a variable pump that is not shown is regulated so that the same only delivers the required quantity of pressure medium. In the first-mentioned publication said pressure is also needed for regulation of the pressure compensators.
By contrast, the object of the disclosure is to provide a control arrangement for a plurality of actuators with which the determination of the pressure of the most highly loaded actuator by means of load sensing lines and changeover valves suitably extending across the valve arrangements and the corresponding transmission to the pump and possibly to the individual pressure compensators can be dispensed with.